[Effects of Festuca arundinacea on the microbial community in crude oil-contaminated saline-alkaline soil]

By using the routine soil physical and chemical analysis methods and the Biolog technique, this paper studied the effects of Festuca arundinacea growth on the pH value, total salt content, and microbial community in the rhizosphere of crude dil-contaminated saline-alkaline soil in Songnen Plain of Northeast China. Crude oil contamination resulted in the increases of average well color development (AWCD), Shannon index (H), and carbon source utilization richness index (S), and altered the utilization patterns of carbon sources by the microbes. F. arundinacea had greater potential to remediate crude oil-contaminated soil. This plant could decrease the soil pH and soil total petroleum hydrocarbon (TPH) content, and increase the soil water content. The AWCD and S in F. arundinacea rhizosphere soil were obviously higher than those in the soil of naked land, providing a suitable environment for the growth and development of rhizosphere soil microbes.

Changes in the chloroplast proteome following water deficit and subsequent watering in a high- and a low-drought-tolerant genotype of Festuca arundinacea

Festuca arundinacea is one of the most drought-tolerant species within the Lolium-Festuca complex and was used as a model for research aimed at identifying the chloroplast components involved in the proteomic response for drought stress in forage grasses. Individual F. arundinacea genotypes with contrasting levels of drought tolerance, the high-drought-tolerant (HDT) and the low-drought-tolerant (LDT) genotypes, were selected for comparative physiological and proteomic work. Measurements of water uptake, chlorophyll fluorescence, relative water content, electrolyte leakage, and gas exchange during drought and rewatering periods were followed by investigations on accumulation levels of chloroplast proteins before drought conditions, on d 3 and 11 of drought treatment, and after 10 d of subsequent watering, using two-dimensional gel electrophoresis. The proteins that were accumulated differentially between the selected plants were then identified by mass spectrometry. The LDT genotype revealed lower levels of water uptake and relative water content as drought progressed, and this was accompanied by lower levels of transpiration and net photosynthesis, and a higher level of electrolyte leakage observed in this genotype. Eighty-two protein accumulation profiles were compared between the HDT and LDT genotypes and ten proteins were shown to be differentially accumulated between them. The functions of the selected proteins in plant cells and their probable influence on the process of recovery after drought treatment in F. arundinacea are discussed.

Hybridization of Neotyphodium endophytes enhances competitive ability of the host grass

• Associations with microbial symbionts may lead to niche differentiation of their host. Vertically transmitted Neotyphodium endophytes of grasses often hybridize in nature. Infection by these hybrid symbionts may result in different host-plant phenotypes from those caused as a result of infection by nonhybrid symbionts. Observations of wild Arizona fescue (Festuca arizonica) populations show that hybrid Neotyphodium-infected (H+) grasses dominate in resource-poor environments, whereas nonhybrid endophyte-infected (NH+) grasses dominate in environments with more resources. We studied the hypothesis that hybridization of endophytes increases stress tolerance of the host. • To test whether hybridization of Neotyphodium affects performance and competitive abilities of the host depending on resources, we conducted a glasshouse experiment where competition, nutrients and watering were manipulated. • H+ plants had greater wet biomass than NH+ and endophyte-free plants, when grown in competition, but only in low-water and low-nutrient treatments. By contrast, NH+ plants did not perform better than H+ or endophyte-free plants regardless of the treatment combination. • Our results suggest that hybridization of symbiotic Neotyphodium endophytes may increase competitive potential of the host in stressful environments and that this hybridization may be underlying niche expansion of Arizona fescue in the environments with low resources.

The effects of cold, light and time of day during low-temperature shift on the expression of CBF6, FpCor14b and LOS2 in Festuca pratensis

Strictly controlled and coordinated induction of CBF regulon (a set of genes regulated by CBF proteins) promotes plant freezing tolerance. CBFs regulate the expression of COR genes that confer freezing tolerance. COR14b in barley is one of the effector genes which seems to be important in resistance to combined freezing and photoinhibition of photosynthesis. LOS2 represses the transcription of STS/ZAT10 (a negative regulator of CBF-target genes) and thus acts as a positive regulator of COR genes. In Arabidopis, low temperature induction of CBFs was reported to be gated by the circadian clock. Moreover, light-quality signals have been shown to regulate some plants' freezing tolerance genes. The aim of our study was to determine the effects of combined treatment with light and cold on the transcript levels of CBF6, FpCor14b and LOS2 genes in Festuca pratensis. We have demonstrated that the regulation of CBF6, FpCor14b and LOS2 induction kinetics in F. pratensis occurs through the interaction of temperature and light with time of day during low-temperature shift. The FpCOR14b transcript level was shown to be up-regulated by increasing light intensity. It was also proved that light quality strongly regulates CBF6, FpCor14b and LOS2 transcripts induction kinetics at low temperatures.

Male-sterile and cleistogamous phenotypes in tall fescue induced by chimeric repressors of SUPERWOMAN1 and OsMADS58

Since tall fescue (Festuca arundinacea Schreb.) is an anemophilous (wind-pollinated) grass species, male sterility is strongly desired for transgenic tall fescue to prevent pollen dispersal. To create male-sterile tall fescue, we applied Chimeric REpressor gene-Silencing Technology (CRES-T) based on rice APETALA3 (AP3) and AGAMOUS (AG) orthologues that specify the formation of stamens. We fused the coding regions of rice AP3 orthologue SUPERWOMAN1 (SPW1), and rice AG orthologues, Os12g0207000, Os01g0886200 and OsMADS58, respectively with the artificial sequence encoding the modified EAR-like motif repression domain (SRDX). We first introduced Os12g0207000SRDX, Os01g0886200SRDX and OsMADS58SRDX into rice for evaluation of their abilities to induce male sterility. The transgenic rice expressing OsMADS58SRDX had reiterated formation of lodicule-like organs instead of stamens and carpel, a typical phenotype of ag mutant. Thus, we found that OsMADS58SRDX was most suitable for our purpose. Next, we introduced SPW1SRDX and OsMADS58SRDX into tall fescue. Although the transgenic tall fescue did not have the stamen alterations seen in SPW1SRDX and OsMADS58SRDX rice, they either produced no pollen or produced immature pollen; thus, the anthers were not dehiscent and the plants were male-sterile. In addition to the male sterility, SPW1SRDX tall fescue showed a cleistogamous (closed) phenotype in which anthers were not observed outside the glumes, with thin, abnormally elongated lodicules. Some lines of OsMADS58SRDX tall fescue showed a cleistogamous phenotype in which the lodicules were homeotically transformed into lemma-like organs. In both cases, cleistogamous phenotype was associated with morphological changes to the lodicules. We also obtained a mild phenotype of OsMADS58SRDX tall fescue, which exhibited only the male sterility. In this study, we produced novel male-sterile phenotypes using chimeric repressors and thus suggest CRES-T as a tool for transgenic improvement of forage and turf grasses.

[Effects of different irrigation minima on green period and cold-resistance physiological indices of Festuca arundinacea]

A pot experiment was conducted to study the effects of different irrigation minima [80% field capacity (FC), 70% FC, 60% FC and 50% FC] from late autumn to early winter on the green period and cold-resistance of Festuca arundinacea. Under the low temperature in winter, treatments 80% FC and 70% FC made the leaf relative water content, POD, CAT, and SOD activities, and chlorophyll, soluble sugar, and free proline contents of F. arundinacea maintained at a higher level, but made the MDA content and electrolyte leakage decreased, resulting in an increased cold-resistance of F. arundinacea. Treatment 80% FC made the green period of F. arundinacea prolonged by 4, 22 and 28 days, as compared with treatments 70% FC, 60% FC, and 50% FC, respectively, and made F. arundinacea have the shortest time to wither in winter and to turn green in spring, with the longest green period. Taking water-saving and water use efficiency into consideration, 70% FC would be the optimum irrigation low limit from late autumn to early winter for F. arundinacea.

Isolation and characterization of a chlorophyll degradation regulatory gene from tall fescue

The non-yellowing gene (NYE1), initially identified from Arabidopsis, is a key regulatory gene responsible for chlorophyll degradation during senescence. Here, FaNYE1, an orthologue of AtNYE1, was further identified from a major type of cool-season turf grass, tall fescue (Festuca arundinacea Schreb.), by RACE-PCR. It consists of 1,441 bp, with an open reading frame of 834 bp, encoding a predicted polypeptide of 278 amino acids. Sequence similarity as well as exon and intron characteristics clearly suggested that FaNYE1 encoded an AtNYE1-like chloroplast protein. FaNYE1 could be strongly induced by dark treatment and natural senescence. FaNYE1, driven by a 1.5 kb upstream fragment of AtNYE1, could rescue the stay-green phenotype of nye1-1. Constitutive overexpression of FaNYE1 in Arabidopsis resulted in the whole spectrum of leaf yellowing phenotypes, the severity of which correlates with its transcript level. These results collectively indicate that FaNYE1 might play an important regulatory role in chlorophyll degradation during senescence in tall fescue, and therefore is a valuable gene for improving the green period or lawn color of turf grasses by genetic engineering.

Adaptive divergence and speciation among sexual and pseudoviviparous populations of Festuca

Pseudovivipary is an environmentally induced flowering abnormality in which vegetative shoots replace seminiferous (sexual) inflorescences. Pseudovivipary is usually retained in transplantation experiments, indicating that the trait is not solely induced by the growing environment. Pseudovivipary is the defining characteristic of Festuca vivipara, and arguably the only feature separating this species from its closest seminiferous relative, Festuca ovina. We performed phylogenetic and population genetic analysis on sympatric F. ovina and F. vivipara samples to establish whether pseudovivipary is an adaptive trait that accurately defines the separation of genetically distinct Festuca species. Chloroplast and nuclear marker-based analyses revealed that variation at a geographical level can exceed that between F. vivipara and F. ovina. We deduced that F. vivipara is a recent species that frequently arises independently within F. ovina populations and has not accumulated significant genetic differentiation from its progenitor. We inferred local gene flow between the species. We identified one amplified fragment length polymorphism marker that may be linked to a pseudovivipary-related region of the genome, and several other markers provide evidence of regional local adaptation in Festuca populations. We conclude that F. vivipara can only be appropriately recognized as a morphologically and ecologically distinct species; it lacks genetic differentiation from its relatives. This is the first report of a 'failure in normal flowering development' that repeatedly appears to be adaptive, such that the trait responsible for species recognition constantly reappears on a local basis.

Identification of candidate genes important for frost tolerance in Festuca pratensis Huds. by transcriptional profiling

Studies of differential gene expression between cold acclimated (CA) and non-cold acclimated (NA) plants yield insight into how plants prepare for cold stress at the transcriptional level. Furthermore genes involved in the cold acclimation process are good candidate loci for genetic variation in frost tolerance and winter survival. In this study we combine different approaches to try to decode the genetics of cold acclimation and frost tolerance in meadow fescue (Festuca pratensis Huds). An EST library of cold acclimation responsive genes was established by suppression subtractive hybridization (SSH), and a microarray experiment was used to identify gene expression differences between high and low frost tolerance genotypes in response to cold acclimation. Many genes known to be involved in CA in other species were confirmed to be involved in CA in F. pratensis, however, 18% of the ESTs did not show significant homology to any database proteins. Seven genes were found to be differentially expressed (>2-fold) between high and low frost tolerance genotypes. Two of these genes, FpQM and FpTPT, represent interesting candidate genes for frost tolerance in perennial forage grasses.

Catechin is a phytototoxin and a pro-oxidant secreted from the roots of Centaurea stoebe

When applied to the roots of Arabidopsis thaliana, the phytotoxin (±)-catechin triggers a wave of reactive oxygen species (ROS), leading to a cascade of genome-wide changes in gene expression and, ultimately, death of the root system. Biochemical links describing the root secreted phytotoxin, (±)-catechin, represent one of most well studied systems to describe biochemically based negative plant-plant interactions, but of late have also sparked controversies on phytotoxicity and pro-oxidant behavior of (±)-catechin. The studies originating from two labs ( 1- 3) maintained that (±)-catechin is not at all phytotoxic but has strong antioxidant activity. The step-wise experiments performed and the highly correlative results reported in the present study clearly indicate that (±)-catechin indeed is phytotoxic against A. thaliana and Festuca idahoensis. Our results show that catechin dissolved in both organic and aqueous phase inflict phytotoxic activity against both A. thaliana and F. idahoensis. We show that the deviation in results highlighted by the two labs ( 1- 3) could be due to different media conditions and a group effect in catechin treated seedlings. We also determined the presence of catechin in the growth medium of C. stoebe to support the previous studies. One of the largest functional categories observed for catechin-responsive genes corresponded to gene families known to participate in cell death and oxidative stress. Our results showed that (±)-catechin treatment to A. thaliana plants resulted in activation of signature cell death genes such as accelerated cell death (acd2) and constitutively activated cell death 1 (cad1). Further, we confirmed our earlier observation of (±)-catechin induced ROS mediated phytotoxicity in A. thaliana. We also provide evidence that (±)-catechin induced ROS could be aggravated in the presence of divalent transition metals. These observations have significant impact on our understanding regarding catechin phytotoxicity and pro-oxidant activity. Our data also illustrates that precise conditions are needed to evaluate the effect of catechin phytotoxicity.

What determines the complex kinetics of stomatal conductance under blueless PAR in Festuca arundinacea? Subsequent effects on leaf transpiration

Light quality and, in particular, its content of blue light is involved in plant functioning and morphogenesis. Blue light variation frequently occurs within a stand as shaded zones are characterized by a simultaneous decrease of PAR and blue light levels which both affect plant functioning, for example, gas exchange. However, little is known about the effects of low blue light itself on gas exchange. The aims of the present study were (i) to characterize stomatal behaviour in Festuca arundinacea leaves through leaf gas exchange measurements in response to a sudden reduction in blue light, and (ii) to test the putative role of Ci on blue light gas exchange responses. An infrared gas analyser (IRGA) was used with light transmission filters to study stomatal conductance (gs), transpiration (Tr), assimilation (A), and intercellular concentration of CO(2) (Ci) responses to blueless PAR (1.80 mumol m(-2) s(-1)). The results were compared with those obtained under a neutral filter supplying a similar photosynthetic efficiency to the blueless PAR filter. It was shown that the reduction of blue light triggered a drastic and instantaneous decrease of gs by 43.2% and of Tr by 40.0%, but a gradual stomatal reopening began 20 min after the start of the low blue light treatment, thus leading to new steady-states. This new stomatal equilibrium was supposed to be related to Ci. The results were confirmed in more developed plants although they exhibited delayed and less marked responses. It is concluded that stomatal responses to blue light could play a key role in photomorphogenetic mechanisms through their effect on transpiration.

Enhanced tolerance of transgenic tall fescue plants overexpressing 2-Cys peroxiredoxin against methyl viologen and heat stresses

Plant 2-Cys peroxiredoxins (2-Cys Prx) has both peroxidase and chaperon function. We overexpressed an Arabidopsis 2-Cys Prx in transgenic tall fescue (Festuca arundinacea) plants to confer tolerance against heat and methyl viologen (MV) stress. Transgenic plants were generated by Agrobacterium-mediated genetic transformation, and integration and expression of the transgene was confirmed by Southern, northern and western blot analyses. Compared to control plants, transgenic plants had significantly less electrolyte leakage and thiobarbituric acid-reactive substances (TBARS) when exposed to heat or MV. Under heat stress (42 degrees C), transgenic plants maintained their chlorophyll fluorescence (Fv/Fm) for 24 h while control plants lost chlorophyll fluorescence very quickly. We conclude that the high levels of 2-Cys Prx proteins in transgenic plants protect leaves from oxidative damage probably due to chaperon activity.

Transcript profiling of the salt-tolerant Festuca rubra ssp. litoralis reveals a regulatory network controlling salt acclimatization

We report an analysis of salt-stress responses in the monocotyledonous halophyte Festuca rubra ssp. litoralis. Salt-dependent expression of transcripts encoding a PIP2;1 aquaporin, V-ATPase subunit B, and the Na+/H+ antiporter NHX was characterized. Transcription of FrPIP2;1, FrVHA-B, and FrNHX1 was induced in root tissue of F. rubra ssp. litoralis by salt treatment, and during salt-stress F. rubra ssp. litoralis accumulated sodium in leaves and roots. Cell specificity of FrPIP2;1, FrVHA-B, and FrNHX1 transcription was analyzed by in situ PCR in roots of F. rubra ssp. litoralis. Expression of the genes was localized to the root epidermis, cortex cells, endodermis, and the vascular tissue. In plants treated with 500 mM NaCl, transcripts were repressed in the epidermis and the outer cortex cells, whereas endodermis and vasculature showed strong signals. These data demonstrate that transcriptional regulation of the aquaporin PIP2;1, V-ATPase, and the Na+/H+ antiporter NHX is correlated with salt tolerance in F. rubra ssp. litoralis and suggests coordinated control of ion homeostasis and water status at high salinity in plants. Salt-induced transcript accumulation in F. rubra ssp. litoralis was further monitored by cDNA-arrays with expressed sequence tags derived from a cDNA subtraction library. The salt-regulated transcripts included those involved in the control of gene expression and signal transduction elements such as a serine/threonine protein kinase, an SNF1-related protein kinase, and a WRKY-type transcription factor. Other ESTs with salt-dependent regulation included transcripts encoding proteins that function in metabolism, general stress responses, and defense and transport proteins.

Taking ecological function seriously: soil microbial communities can obviate allelopathic effects of released metabolites

BACKGROUND

Allelopathy (negative, plant-plant chemical interactions) has been largely studied as an autecological process, often assuming simplistic associations between pairs of isolated species. The growth inhibition of a species in filter paper bioassay enriched with a single chemical is commonly interpreted as evidence of an allelopathic interaction, but for some of these putative examples of allelopathy, the results have not been verifiable in more natural settings with plants growing in soil.

METHODOLOGY/PRINCIPAL FINDINGS

On the basis of filter paper bioassay, a recent study established allelopathic effects of m-tyrosine, a component of root exudates of Festuca rubra ssp. commutata. We re-examined the allelopathic effects of m-tyrosine to understand its dynamics in soil environment. Allelopathic potential of m-tyrosine with filter paper and soil (non-sterile or sterile) bioassays was studied using Lactuca sativa, Phalaris minor and Bambusa arundinacea as assay species. Experimental application of m-tyrosine to non-sterile and sterile soil revealed the impact of soil microbial communities in determining the soil concentration of m-tyrosine and growth responses.

CONCLUSIONS/SIGNIFICANCE

Here, we show that the allelopathic effects of m-tyrosine, which could be seen in sterilized soil with particular plant species were significantly diminished when non-sterile soil was used, which points to an important role for rhizosphere-specific and bulk soil microbial activity in determining the outcome of this allelopathic interaction. Our data show that the amounts of m-tyrosine required for root growth inhibition were higher than what would normally be found in F. rubra ssp. commutata rhizosphere. We hope that our study will motivate researchers to integrate the role of soil microbial communities in bioassays in allelopathic research so that its importance in plant-plant competitive interactions can be thoroughly evaluated.

Identification of leaf proteins differentially accumulated during cold acclimation between Festuca pratensis plants with distinct levels of frost tolerance

Festuca pratensis (meadow fescue) as the most frost-tolerant species within the Lolium-Festuca complex was used as a model for research aimed at identifying the cellular components involved in the cold acclimation (CA) of forage grasses. The work presented here also comprises the first comprehensive proteomic research on CA in a group of monocotyledonous species which are able to withstand winter conditions. Individual F. pratensis plants with contrasting levels of frost tolerance, high frost tolerant (HFT) and low frost tolerant (LFT) plants, were selected for comparative proteomic research. The work focused on the analysis of leaf protein accumulation before and after 2, 8, and 26 h, and 3, 5, 7, 14, and 21 d of CA, using high-throughput two-dimensional electrophoresis, and on the identification of proteins which were accumulated differentially between the selected plants by the application of mass spectrometry. The analyses of approximately 800 protein profiles revealed a total of 41 (5.1%) proteins that showed a minimum of a 1.5-fold difference in abundance, at a minimum of one time point of CA for HFT and LFT genotypes. It was shown that significant differences in profiles of protein accumulation between the analysed plants appeared relatively early during cold acclimation, most often after 26 h (on the 2nd day) of CA and one-half of the differentially accumulated proteins were all parts of the photosynthetic apparatus. Several proteins identified here have been reported to be differentially accumulated during cold conditions for the first time in this paper. The functions of the selected proteins in plant cells and their probable influence on the level of frost tolerance in F. pratensis, are discussed.

Atmospheric vapor pressure deficit is critical in predicting growth response of "cool-season" grass Festuca arundinacea to temperature change

There is a lack of information on plant response to multifactor environmental variability including the interactive response to temperature and atmospheric humidity. These two factors are almost always confounded because saturated vapor pressure increases exponentially with temperature, and vapor pressure deficit (VPD) could have a large impact on plant growth. In this study using climate controlled mini-greenhouses, we examined the interacting influence of temperature and VPD on long-term growth of tall fescue (Festuca arundinacea Schreb), a cool season grass. From past studies it was expected that growth of tall fescue would decline with warmer temperatures over the range of 18.5-27 degrees C, but growth actually increased markedly with increasing temperature when VPD was held constant. In contrast, growth declined in experiments where tall fescue was exposed to increasing VPD and temperature was held constant at 21 degrees C. The inhibited growth appears to be in response to a maximum transpiration rate that can be supported by the tall fescue plants. The sensitivity to VPD indicates that if VPD remains stable in future climates as it has in the past, growth of tall fescue could well be stimulated rather than decreased by global warming in temperate climate zones.

[Ecophysiological responses of Festuca arundinacea to high temperature stress]

The measurement of leaf relative water content (RWC), chlorophyll content, cell membrane lipid peroxidation, anti-oxidative system, and photosynthesis of two F. arundinacea cultivars (Barlexas and Crossfire II) and Cynodon dactylon under high temperature (38 degrees C / 30 degrees C, day/ night) showed that with the increasing time of exposure to high temperature, the leaf RWC, chlorophyll content, net photosynthetic rate (P(n)) and photochemical efficiency (F(v)/F(m)) of two F. arundinacea cultivars had a decreasing trend, and the average decrement was smaller for Barlexas than for Crossfire II. After exposed to high temperature for 9 days, the average activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in Barlexas leaves were 19.7%, 17.9% and 17.7% higher than those in Crossfire II leaves, and the P(n) of Barlexas and Crossfire II was decreased by 60.7% and 81.9%, respectively. Under high temperature, the F(v)/F(m) of Barlexas leaves was higher than that of Crossfire II leaves, which could be helpful to mitigate the damage of high temperature to the photosynthetic apparatus of Barlexas. No significant change was observed for each test physiological parameter of C. dactylon leaves with the increase of exposure time under high temperature. The adaptation ability to high temperature was in the order of C. dactylon > Barlexas > Crossfire II.

Overexpression of AeNHX1, a root-specific vacuolar Na+/H+ antiporter from Agropyron elongatum, confers salt tolerance to Arabidopsis and Festuca plants

Agropyron elongatum, a species in grass family, has a strong tolerance to salt stress. To study the molecular mechanism of Agropyron elongatum in salt tolerance, we isolated a homolog of Na(+)/H(+) antiporters from the root tissues of Agropyron plants. Sequence analysis revealed that this gene encodes a putative vacuolar Na(+)/H(+) antiporter and was designated as AeNHX1. The AeNHX1-GFP fusion protein was clearly targeted to the vacuolar membrane in a transient transfection assay. Northern analysis indicated that AeNHX1 was expressed in a root-specific manner. Expression of AeNHX1 in yeast Na(+)/H(+) antiporter mutants showed function complementation. Further, overexpression of AeNHX1 promoted salt tolerance of Arabidopsis plants, and improved osmotic adjustment and photosynthesis which might be responsible for normal development of transgenic plants under salt stress. Similarly, AeNHX1 also functioned in transgenic Festuca plants. The results suggest that this gene might function in the roots of Agropyron plants, and its expression is involved in the improvement of salt tolerance.

Herbivore specific induction of silica-based plant defences

Induced plant responses to herbivory have major impacts on herbivore feeding behaviour, performance and population dynamics. These effects are well established for chemical defences, but induction of physical defences remains far less studied. However, for many plants, it is physical defences that play the major role in regulating the levels of herbivore damage sustained. We provide evidence that, in grasses, induction of physical defences is both specific to herbivore feeding, as opposed to mechanical damage, and may be dependant on the amount of damage imposed. Furthermore, we show that the magnitude of the induction response is sufficient to deter further damage and affect herbivore performance. We compared silica induction in two grass species in response to vertebrate and invertebrate damage, and to mechanical defoliation. Induction was assessed at two levels of damage over 16 months. Foliar silica content did not increase in response to mechanical defoliation, but damage by either voles or locusts resulted in increases in silica content of over 400%. This increase deterred feeding by both voles and locusts. Silica induction in grasses due to repeated damage events over a prolonged period suggests a possible role for silica defence in the cyclical population fluctuations observed in many grass-feeding herbivores.

Root foraging traits and competitive ability in heterogeneous soils

The responses of plant roots to nutrient patches in soil may be an important component of competitive ability. In particular, the scale, precision, and rate of foraging for patchy soil resources may influence competitive ability in heterogeneous soils. In a target-neighbor experiment in the field, per-individual and per-gram competitive effects were measured for six old-field species with known root foraging scale, precision, and rate. The presence and number of nutrient patches were also manipulated in a full factorial design. Number and presence of patches did not influence the outcome of competition. Competitive ability was not related to total plant size, growth rate, or root:shoot allocation, or to root foraging precision. Per-individual competitive effects were marginally correlated with root foraging scale (biomass of roots) and root foraging rate (time required to reach a patch). Therefore, competitive ability was more closely related to ability to quickly fill a soil volume with roots than to ability to preempt resource-rich patches.

Cross-species identification of Mendel's I locus

A key gene involved in plant senescence, mutations of which partially disable chlorophyll catabolism and confer stay-green leaf and cotyledon phenotypes, has been identified in Pisum sativum, Arabidopsis thaliana, and Festuca pratensis by using classical and molecular genetics and comparative genomics. A stay-green locus in F. pratensis is syntenically equivalent to a similar stay-green locus on rice chromosome 9. Functional testing in Arabidopsis of a homolog of the rice candidate gene revealed (i) senescence-associated gene expression and (ii) a stay-green phenotype after RNA interference silencing. Genetic mapping in pea demonstrated cosegregation with the yellow/green cotyledon polymorphism (I/i) first reported by Gregor Mendel in 1866.

Model systems in ecology: dissecting the endophyte-grass literature

Model systems can facilitate and focus research efforts but ill-chosen or inapt ones can distract or impede scientific progress. In this Opinion article, we pose the question: how can the literature provide appropriate general conclusions if the model systems upon which the literature is based are unrepresentative of the relevant biological diversity? A good example of this problem is the endophyte-grass symbiosis, which is considered to be a classic example of mutualistic interactions. Meta-analysis of the primary literature demonstrates that the conceptual framework for endophyte-grass interactions has largely been based on endophyte-plant-herbivore studies of two agricultural grass species, tall fescue and perennial ryegrass. Consistent with conventional wisdom, the meta-analysis indicates that endophytes slightly increase grass resistance to herbivores. By contrast, endophytes appear not to affect plant performance or competitive ability. The positive effects of endophytes appear to be dependent on genetic variation in the host and endophyte, and on nutrient availability in soils. Thus, the agronomic grass model systems fail to capture the breadth of variability inherent in wild grass-endophyte populations and communities.

Lifetime reproductive success and density-dependent, multi-variable resource selection

Individuals are predicted to maximize lifetime reproductive success (LRS) through selective use of resources; however, a wide range of ecological and social processes may prevent individuals from always using the highest-quality resources available. Resource selection functions (RSFs) estimate the relative amount of time an individual spends using a resource as a function of the proportional availability of that resource. We quantified the association between LRS and coefficients of individual-based RSFs describing lifetime resource selection for 267 female red deer (Cervus elaphus) of the Isle of Rum, Scotland, from 1970 to 2001. LRS was significantly related to first- and second-order effects of selection for Agrostis/Festuca grassland and proximity to the sea coast (quality of forage within Agrostis/Festuca grassland was highest nearest the coast (ratio of short:long grassland)). The benefits of selecting for quality in Agrostis/Festuca grassland, however, traded-off with increases in LRS gained by avoiding conspecific density. LRS was inversely associated with local density, which was highest along the coast, and reproductive benefits of selecting Agrostis/Festuca grassland diminished with increasing density. We discuss the relevance of these results to our understanding of the spatial distribution of red deer abundance, and potential applications of our approach to evolutionary and applied ecology.

Germination Responses to GA3 and Stratification of Threatened Festuca L. Species from Eastern Mediterranean

The seed germination characteristics of three threatened Festuca sp. [F. punctoria Sm., F. cyllenica Boiss. et Heldr. subsp. uluana Markgr.-Dannenb., F. paphlagonica (St.-Yves) Markgr.-Dannenb. subsp. paphlagonica] were investigated. These species are endemic and spread on alpine belt. The study was carried out with wet-cold and dry-cold stratification throughout 15 days, different doses of GA3 (50, 100 and 150 ppm) and hormone-stratification combined treatments, and non-treatment series. We found that the germination rates of three fescue seeds for various treatment series were different. The mean germination percentage of F. cyllenica was higher (80%) than that of F. punctoria and F. paphlagonica which were fairly low (50-60%). Germination rates increased by wet-stratification treatment in F. punctoria and also increased with 100 ppm GA3 application to the seeds of F. paphlagonica. When taken into consideration the germination percentages of all fescue species, the seeds of F. punctoria and F. paphlagonica can be dormant, but the seeds of F. cyllenica are non-dormant.

GISH/FISH mapping of genes for freezing tolerance transferred from Festuca pratensis to Lolium multiflorum

The first backcross breeding programme for the transfer of freezing-tolerance genes from winter hardy Festuca pratensis to winter-sensitive Lolium multiflorum is described. A partly fertile, triploid F(1) hybrid F. pratensis (2n=2x=14) x L. multiflorum (2n=4x=28) was employed initially, and after two backcrosses to L. multiflorum (2x) a total of 242 backcross two (BC(2)) plants were generated. Genomic in situ hybridisation (GISH) was performed on 61 BC(2) plants selected for their good growth and winter survival characters in the spring following one Polish winter (2000-2001). Among the winter survivors, diploid chromosome numbers were present in 80% of plants. An appropriate single Festuca introgression in an otherwise undisturbed Lolium genome could provide increased freezing tolerance without compromise to the good growth and plant vigour found in Lolium. Among all the diploids, a total of 20 individuals were identified, each with a single F. pratensis chromosome segment. Another diploid plant contained 13 Lolium chromosomes and a large metacentric F. pratensis chromosome, identified as chromosome 4, with two large distal Lolium introgressions on each chromosome arm. Three of the diploid BC(2), including the genotype with Festuca chromosome 4 DNA sequences, were found to have freezing tolerance in excess of that of L. multiflorum, and in one case in excess of the F. pratensis used as control. A detailed cytological analysis combining GISH and fluorescence in situ hybridisation analyses with rDNA probes revealed that the other two freezing-tolerant genotypes carried a Festuca chromosome segment at the same terminal location on the non-satellite arm of Lolium chromosome 2.